1. Technical Field
The present invention relates to an illumination device and a projector.
2. Related Art
The development of projectors using an array of light sources with plural semiconductor light emitting devices is being advanced. Known semiconductor light emitting devices include, for example, a semiconductor laser (laser diode), a super luminescent diode (hereinafter, may be referred to as “SLD”), an LED (light emitting diode), and an OLED (organic light emitting diode).
Among these devices, the SLD has a slight disadvantage with respect to light output, but has the advantage of an inherently smaller speckle noise due to the presence of a different gain region structure as compared to a semiconductor laser. However, due to a nonresonant structure in which the gain region is provided at a tilt with respect to an end surface (output surface) of a substrate with the semiconductor light emitting device formed thereon, the output light has an angular distribution with low symmetry similar to a crescent shape.
Generally, many light modulation devices used for projectors have display properties dependent on the incident angles of incident illumination light. Accordingly, to realize a projection image with high image quality, it is desirable to use illumination light having high angular distribution symmetry (which may be referred to as “symmetry of sectional shape of light”) and a uniform intensity distribution. This is because angular distribution asymmetry and intensity distribution nonuniformity cause brightness irregularities and contrast irregularities.
For example, International Publication WO 99/49358 discloses an optical configuration that illuminates an image display device by using a light emitter in which plural semiconductor lasers are arranged in a two-dimensional array and parallelizing a beam output from the light emitter. In a typical edge-emitting semiconductor laser, the gain region is formed perpendicularly to the substrate end surface, the output light has an oval sectional shape, and the angular distribution has high symmetry. Accordingly, the output light from the light emitter may be converted into parallel light relatively easily and an optical switch (light modulation device) may be illuminated with light having a nearly uniform intensity distribution.
However, in the configuration of International Publication WO 99/49358, if the semiconductor lasers are simply replaced with SLDs, the angular distributions of the output light are very different due to the difference in the gain region structure between the semiconductor lasers and the SLDs as described above, and thus, it is difficult to obtain a desired illumination condition.